A nonconcurrent prospective study is proposed to determine whether patients with a deep venous thrombosis or pulmonary embolism and no obvious malignancy at the time of diagnosis have an increased incidence of cancer in the years following the thrombosis. All Olmsted County patients who have had venograms, pulmonary angiograms, or lung scans performed to detect deep vein thrombosis or pulmonary emboli at the Mayo Clinic-affiliated hospitals in the years 1964 through 1983 will be the subjects of the study. All patients will be followed until death or the completion of the study. Patients with procedures indicating the presence and the absence of deep vein thrombosis or pulmonary embolism will be compared, looking specifically for subsequent occurrence of cancers. For both groups expected rates for total and specific type of malignancy will also be calculated, using Olmsted County population-based data, supplemented as necessary with other population-based reports (e.g. Connecticut Tumor Registry, 3rd National Cancer Survey, SEER data). If patients with deep vein thrombosis or pulmonary embolism do have an increased risk of subsequent detection of cancer, they should have careful followup with use of current screening modalities.